My best friend has a 911 GT3. Compared to the GTR it's way way different. The Gt3 is a straight up race car. Hardly and electronics. You really get the feeling that YOU are the one controlling the car. It will get sideways in a snap of a finger. It truly is a joy to drive, amazing steering, handling, and brakes. Power wise...it rips, considering it's a n/a 6 cylinder.
I saw one of my old high school buddies over the summer. He has a 2010 GTR. He let me take it for a spin. The car has intake, exhaust, down pipes, and a tune. It straight up rips.....The car is much more computer controlled, and you can feel the awd making corrections for you around turns. But the car really handles like a bad mofo, and has wicked acceleration.
Take a look at AMS Alpha GTR, hahaah, its INSANE. Destroys almost everything, from zr1vettes, to viper's, and pretty much all exotics.